1. Field of the Invention
This invention relates to an isolation container for use with a downhole electric pump and the method of its application. The downhole electric pump is of the type used in the oil and gas industry. Such pumps usually are used for pumping oil and gas production to the surface when naturally occurring formation pressure is insufficient to raise the oil and gas to the surface. However, downhole electric pumps are also used in a downhole environment to increase the pressure of pressurized and un-pressurized fluids supplied from the surface. In these instances, the pressurized fluid is injected into the adjacent oil and gas bearing formation to treat or xe2x80x9cfracturexe2x80x9d the formation. In other applications, a downhole electric pump pressurizes fluid for injection into a formation to urge oil in the area of the wellbore in the direction of another nearby well where the oil is more easily produced. In these operations, any number of wells may be used to xe2x80x9cchasexe2x80x9d the underground oil to the collecting well. FIG. 1 is a sectional view of a prior art configuration utilizing a downhole electric pump assembly to inject high pressure fluid into a formation. The prior art configuration of FIG. 1 has a surface platform 10 (shown schematically) extending above ocean surface 12. Production riser 14 extends downwardly to hydraulically actuated connector 16 which is sealingly connected to wellhead housing 18 in a manner well known to those of ordinary skill in the art. Casing 20 extends from wellhead housing 18 to subsurface formation 22 and is cemented in place in ocean floor 24. Production tubing 26 extends from surface platform 10 through wellhead housing 18 to downhole packer 28 positioned in casing 20. Extension nipple 30 and coupling 32 connect production tubing 26 to downhole electric pump assembly 34. Lower extension nipple 36 extends from downhole electric pump assembly 34 through lower downhole packer 38 to that area of the wellbore adjacent subsurface formation 22. Downhole electric pump assembly 34 includes electric motor 40, motor seal section 41 and downhole electric pump 42. Electrical cable 44 extends from the surface to electric motor 40 in a manner well known to those of ordinary skill in the art.
A typical sequence of operation has fluid 46 supplied from surface platform 10 through production tubing 26 to downhole electric pump assembly 34 where it is taken into the pump assembly through intake ports 35. Thereafter, downhole electric pump assembly 34 increases the pressure of fluid 46 and then discharges it through lower extension nipple 36 into subsurface formation 22. In this manner, pressurized fluid 46 may be used to cause fracturing of the subsurface formation 22 to increase production capacity or it can be used to urge oil to another area of a field for collection at another well.
There are problems associated with prior art electric pumps used in a wellbore. As is visible in the apparatus of FIG. 1, the fluid for injection into the formation 22 must first be deposited in an annular area between the pump intake ports 35 and the well casing wall 20, subjecting the well casing 20 to any fluid used in the injection operation. Fluids used in these operations are often corrosive. For example, a fracturing operation can utilize additives like surfactants and acidizing fluids. In cases where water is injected into a formation, the water itself, especially sea water, can be corrosive. In those cases where the pressure of a fluid is increased at the well surface and then boosted by the downhole pump, the casing wall is subjected to the pressure of the fluid. Continued exposure of casing wall to the effects of corrosive and high pressure fluids can lead to a collapse of the casing well and ultimate exposure of the wellbore to the surrounding elements.
2. Background of the Related Art
U.S. Pat. No. 5,203,682 to B. A. Inklebarger shows a submersible pump assembly mounted in a container for use at the surface for pressurizing fluid.
The modular pump shown in U.S. Pat. No. 5,626,467 to G. A. Cantey discloses a fluid driven by an air motor.
U.S. Pat. No. 5,799,834 to D. D. Small et al. shows an adjustable length column pipe for connecting a submersible electric pump in a fuel storage tank to dispenser units.
The isolation container of the present invention is designed for use with a downhole electric pump or other electrical pump commonly used in oil and gas drilling and production operations. The isolation container includes an annular vessel with an axial inlet and outlet bore. A downhole electric pump is centrally located within the isolation container. The downhole electric pump includes an electric motor positioned above and coupled to a motor seal section, which is then coupled to a centrifugal pump, thereby providing a means of powering the pump. A blind coupling is positioned above the electric motor with a tubular member connected thereto and extending through the inlet of the isolation container. The tubular member connects to a tubing string supplying fluid from the surface. The blind coupling has a plurality of radially disposed ports to allow fluid from the surface to flow into the annulus between the downhole electric pump and the isolation container. This fluid then flows to inlet ports on the downhole electric pump. The pressure of the fluid is increased or boosted by the operation of the downhole electric pump and the fluid is discharged through a tubular member, which is sealed in the outlet bore of the isolation container. The tubular member extends through a packer positioned below the isolation container and the pressurized fluid is injected into the desired subsurface formation or zone for fracturing or for displacing oil towards an adjacent formation. An electrical cable from the surface supplies power to the electric motor and a check valve may be provided on the upper end of the isolation container for releasing entrained air in the isolation container. The container effectively isolates the casing well of the well from the harmful effects of the fluid pumped by the pump.
A second embodiment using the isolation container of the present invention is disclosed. This embodiment uses the isolation container with an downhole electric pump commonly used in oil and gas drilling and production operations to inject a treatment fluid into a subsurface formation. The isolation container has the same construction as in the first embodiment. The tubing string above the isolation container has a remotely operable valve, such as by wireline, disposed in its bore. The tubing string extends above the isolation container typically is 200 to 500 feet in length and is filled with the fluid to be used in the operation. The top of tubing string is capped and electrical cable or xe2x80x9cExe2x80x9d line as it referred to in the industry is attached to the cap. The xe2x80x9cExe2x80x9d line is of the type commonly deployed from a wireline truck and typically is xc2xexe2x80x3 in diameter. The wireline truck is used to lower the tubing string and isolation container into position. As in the first embodiment, a blind coupling is positioned above the electric motor with a tubular member connected thereto and extending through the inlet of the isolation container. The blind coupling has a plurality of radially disposed ports to allow the fluid from the tubing string to flow into the annulus between the downhole electric pump and the isolation container when the tubing string valve is opened. The fluid then flows to inlet ports on the downhole electric pump. The pressure of the fluid is then increased or boosted by the operation of the downhole electric pump. The fluid is then discharged through a tubular member, which is sealed in the outlet bore of the isolation container. The tubular member extends through a packer positioned below the isolation container and the boosted pressure fluid is injected into the desired subsurface formation or zone for acidizing. The aforementioned xe2x80x9cExe2x80x9d line is extended along the outside of the tubing string and supplies power to the electric motor.
These with other objects and advantages of the present invention are pointed out with specificness in the claims annexed hereto and form a part of this disclosure. A full and complete understanding of the invention may be had by reference to the accompanying drawings and description of the preferred embodiments.